DE 10 2004 018 104 A1 discloses a discharge lamp which has a discharge vessel which is helical, at least in regions. Tubular pieces can be fitted as pump tubes to this discharge vessel. Pump tubes such as these are used on the one hand to hold a mercury source. By way of example, this may be an amalgam sphere.
Another function of a pump tube is to make it possible to evacuate the discharge vessel and to fill it with an appropriate filling gas via the pump tube during the production of the lamp. A further function which a pump tube can carry out can be considered that of offering the capability for purging the discharge vessel. Furthermore, if it has a sufficiently large cross section, the tubular piece can offer good access capabilities to the discharge vessel, for example in order to introduce the mercury source.
Furthermore, EP 1 282 153 A2 discloses a discharge vessel for a discharge lamp. The inner face of the discharge vessel is coated with a protective layer and with a fluorescent layer. The protective layer is applied directly to the inner face of the discharge vessel and, for example, may be an AlonC layer.
In order to fit the tubular piece, or the pump tube, to the discharge vessel it is necessary for the inner face of the discharge vessel to be wiped free cleanly at the connection point, as a result of which the protective layer is no longer present. This is because, in the connection area between the tubular piece and the discharge vessel, the material of the protective layer actually contributes to the capability to provide sudden changes in the glazing between the pump tube and the discharge vessel.
Since the geometries and configurations of the discharge vessels mean that the process of wiping free can be carried out only at accessible points, the connection between the tubular piece and the discharge vessel can also be made only at a small number of specific points. Furthermore, the process of wiping free at the attachment point is time-consuming, and is associated with a further manufacturing step. This lengthens the manufacturing time and, furthermore, also therefore increases the costs.